The present invention relates to mechanical devices employing screw-like threaded configurations and, in particular, it concerns an apparatus which provides a variable pitch thread.
A multitude of devices employ elements with a helical thread, such as screws and bolts, for a range of different functions including adjustment, attachment and generating motion. Some devices employ helical channels for flow regulation. Others employ rotating rods with helical flanges to act as a conveyor for various materials. In certain cases the helix is right-handed while in others a left-handed helix is used.
In all cases known to the applicant, all such helical configurations, referred to herein generically as xe2x80x9cthreadedxe2x80x9d configurations, have a fixed pitch. In other words, the step traveled by an object engaged with the thread during a single 360xc2x0 revolution of the structure, equal to the distance between adjacent turns of the thread, has a single fixed value determined during manufacture and which cannot later be varied.
It would be highly advantageous for a wide range of applications to provide a thread configuration which would allow the pitch of the thread to be varied.
The present invention is an apparatus with a variable pitch thread.
According to the teachings of the present invention there is provided, an apparatus comprising: (a) a hollow cylindrical element having a first end, a second end and defining a virtual central axis, the cylindrical element being configured to provide a plurality of parallel, radially projecting ridges extending circumferentially around the cylindrical element and spaced apart with a given step as measured parallel to the central axis, the cylindrical element further featuring a slit extending substantially parallel to the central axis from the first end to the second end, the slit being bordered by opposing edges; and (b) an actuation mechanism configured to selectively generate controlled relative displacement between the opposing edges so as to vary a helical angle of the projecting ridges relative to the central axis.
According to a further feature of the present invention, the actuation mechanism is configured to relatively displace the opposing edges such that the plurality of projecting ridges together form alternatively a helical pattern and a pattern of substantially closed rings.
According to a further feature of the present invention, the actuation mechanism is configured to apply a torque between the first and second ends about the central axis.
According to a further feature of the present invention, the cylindrical element is configured such that, in the absence of an externally applied torque, each of the radially projecting ridges approximates to a closed circumferential ridge.
According to a further feature of the present invention, the cylindrical element is configured such that, in the absence of an externally applied torque, the plurality of radially projecting ridges together approximate to a single threaded configuration.
According to a further feature of the present invention, the radially projecting ridges project radially inwards. According to an alternative, or additional, feature of the present invention, the radially projecting ridges project radially outwards.
According to a further feature of the present invention, there is also provided a rider mounted on the cylindrical element, the rider having at least one engagement feature configured for interlocking engagement with at least part of at least two of the radially projecting ridges.
According to a further feature of the present invention, the rider is implemented as a complementary cylindrical member having a longitudinal slit such that, when the longitudinal slit is aligned substantially opposite the slit of the cylindrical element, the rider conforms substantially to the helical angle.
According to a further feature of the present invention, the rider is implemented as a complementary cylindrical threaded member with a fixed helical angle such that, when the helical angle of the projecting ridges assumes a first value, the rider can be readily rotated relative to the cylindrical element bout the central axis and, when the helical angle of the projecting ridges assumes a second value, the rider is locked against rotation relative to the cylindrical element.
There is also provided according to the teachings of the present invention, a flow-regulating configuration comprising: (a) the aforementioned apparatus; and (b) a cylindrical surface deployed adjacent to the plurality of radially projecting ridges so as to define a variable pitch flow channel between the cylindrical element and the cylindrical surface.
There is also provided according to the teachings of the present invention, a method for producing a variable pitch thread comprising the steps of: (a) providing a hollow, cylindrical element having a first end, a second end and defining a virtual central axis, the cylindrical element being configured to provide a plurality of parallel, radially projecting ridges extending circumferentially around the cylindrical element and spaced apart with a step a as measured parallel to the central axis, the cylindrical element further featuring a slit extending substantially parallel to the central axis from the first end to the second end, the slit being bordered by opposing edges; and (b) relatively displacing the opposing edges so as to vary a helical angle of the projecting ridges relative to the central axis.